There is a strong drive to reduce unnecessary power used in the wireless communication networks, such as e.g. Global System for Mobile Telecommunications (GSM) networks or Wideband Code Division Multiple Access (WCDMA), primarily due to energy efficiency reasons.
One suggestion is to reduce the output power of the Broadcast Control Channel (BCCH) carrier. As transmissions are made over the BCCH twenty-four hours, all around the year, also a small reduction of output power may result in large power savings aggregated over time. However, operators are reluctant to reduce BCCH power, since they are afraid of loosing coverage. In GSM the power of the BCCH carrier defines the cell border towards the noise floor.
It has been suggested to reduce the BCCH power for capacity cells. That is, for cells with no traffic close to the noise floor, for example, cells covering a park in a city or a cell covering a football stadium. Since the BCCH carrier is transmitting all the time, a large proportion of the power used on a site is to provide the BCCH carrier.
Another problem in today's GSM networks is that operators have very little information about where coverage holes are for mobile phones that are in idle mode. In active mode there are many different ways to know where radio traffic has poor coverage.
Statistics exists for Circuit Switched (CS) traffic that is in active mode, i.e. have a call up and running. Here it is possible to monitor if the traffic have good signal strength or not with tools that log e.g. measurement reports and/or other signalling that takes place in active mode. A mobile phone that have a CS call ongoing in GSM will transmit four signalling bursts every 480 ms to the base station, where the received signal burst is derived into a measurement report. However, there is no information about mobile phones that are in idle mode.
For Packet Switched (PS) traffic there are limited possibilities to monitor the signal strength of the traffic. In Packet Transfer Mode there will be information reported by the handset that show what signal strength a connection has. In Packet Idle mode there is no information about signal strength.
Also, a human user may, due to human behaviourism develop a conditioned reflex to avoid coverage holes e.g. by not letting the mobile phone enter active mode in a place where he/she knows the coverage is bad, e.g. in the basement within a building, and instead move to the upper floor before making a phone call, or leave the mobile phone on the upper floor when going down in the basement. Thus by e.g. counting the number of lost connections in active mode does not necessarily give an appropriate picture of the coverage situation in idle mode.
With better knowledge about coverage holes within a wireless communication network, it is possible to build sites and/or adjust transmission power of base stations and/or add nodes to improve coverage.
A GSM mobile in idle mode can “lose coverage” and according to the specifications 3GPP TS 23.122 and 3GPP TS 24.008, a mobile user camping on its home Public Land Mobile Network (PLMN) will not signal when it returns to coverage unless the cell it re-enters in another Location Area or the timer T3212 has expired.
In 3GPP TR 36.805, the minimization of drive tests is discussed and more advanced ideas are discussed.
The operators have problem to know when a GSM mobile phone in idle mode goes out of coverage and comes back into coverage. Cell planning tools may not give enough accuracy and these tools may not have all information about the real traffic.